1. Field of the Invention
This invention relates to an inductive type thin film magnetic head for recording with a combination read/write thin film magnetic head that is used for a floating type magnetic head, especially to a combination read/write thin film magnetic head in which a lower core layer serving also as an upper shielding for a readout magnetoresistive element and a coil layer formed on the lower core layer via an insulating layer can be constantly formed, and which allows an improvement in selectivity of soft magnetic materials by forming the lower core layer by a spattering method, and a method for manufacturing the same.
2. Description of the Related Art
FIG. 5 is an enlarged sectional view of a conventional combination read/write thin film magnetic head viewed along the opposite direction of the recording medium.
The layer of the magnetoresistive element 1 is composed of three layers, laminating a soft magnetic layer (a soft adjacent layer; SAL), non-magnetic layer (a SHUNT layer) and a magnetoresistive layer (a MR layer) from the lower to the upper, respectively. Usually, the magnetoresistive layer (MR layer) is a layer of Fe--Ni alloy (permalloy) and the non-magnetic layer (SHUNT layer) is a layer of tantalum (Ta), and the soft magnetic layer is formed with a Ni--Fe--Nb alloy.
A lower gap layer 3 comprising a non-magnetic material like aluminum oxide (Al.sub.2 O.sub.3) is formed on the lower shielding layer 2 composed of sendust or permalloy as shown on the figure, on which a layer of the magnetoresistive layer 1 is formed. Hard bias layers 4 are formed as longitudinal bias layers at both sides of the magnetoresistive layer 1. A main lead layer 5 comprising non-magnetic electrically conductive materials like copper (Cu) or tungsten (W) is formed on the hard bias layer 4 described above. An upper gap layer 6 of a non-magnetic material like aluminum oxide (Al.sub.2 O.sub.3) is further formed on the main lead layer, forming a buffer layer (not shown) on the upper gap layer 6 described above. The buffer layer described above can be formed by sputtering magnetic materials like Fe--Ni alloy (permalloy). A lower core layer 13 is formed on the lower layer described above by plating, for example, permalloy.
A non-magnetic layer 14 comprising aluminum oxide is formed on the lower core layer 13, on which a coil layer 9 formed in a flat spiral pattern is provided via an organic insulating layer. An upper core layer 10 is formed on a layer of non-magnetic material 14 at a position confronting the lower core layer 13. This upper core layer 10 is also formed by plating permalloy as in the lower core layer 13 described above. A protecting layer 11 comprising aluminum oxide is provided on the upper core layer 10.
The layers from the lower core layer 13 to the protective layer 11 serve for signal recording, composing an inductive head. In this inductive head, a recording current is applied to the coil layer 9 so that a recording magnetic field is imparted to the layers from the coil layer 9 to the upper core layer 10 and to the lower core layer 13. Magnetic signals can be recorded on a recording medium like a hard disk by a fringing magnetic filed between the lower core layer 13 and upper core layer 10. In the combination read/write thin film magnetic head in which a read out part with a layer of the magnetoresistive element 1 and inductive head described above are laminated, the lower core layer 13 composing an inductive head also serves as an upper shielding layer in the read out part having a layer of the magnetoresistive element 1 as shown in FIG. 5.
In the inductive head described above, it is required for a high density recording in a recording medium that the gap distance of the magnetic gap G described above should be as short as possible. Therefore, the layer of the non-magnetic material 14 is formed as thin as possible.
In the prior art as shown in FIG. 5, however, there were problems as describe below because the lower core had been formed by plating, for example, permalloy.
(A) A terrace A is formed at both edges of the lower core layer 13 because the lower core layer 13 is thick and the cross sectional configuration of the lower core layer 13 assumes a rectangle. Therefore, making the thickness of the non-magnetic material 14 formed on the lower core layer 13 uniform is so difficult that the thickness of the non-magnetic material 14 becomes extremely thin in the vicinity of the side edges of the lower core layer 13, sometimes causing a failure of electric insulation between the lower core layer 13 and coil layer 9. Especially, when the clearance between the lower core layer 13 and upper core layer 10 is narrowed for making the gap width small in order to increase the recording density, pin holes are liable to appear on the non-magnetic material 14 at the terrace A described above because the thickness of the non-magnetic material 14 becomes too thin.
(B) A terrace is also formed on the surface of the non-magnetic material 14 above the terrace A because the cross sectional configuration of the lower core layer 13 is a rectangle forming a terrace A at both side edges. Therefore, the coil layer 9 is formed on the terrace of the non-magnetic material 14 when the area of the lower core layer 13 is smaller than the area where the coil layer 9 is formed, thereby making it difficult to form the coil layer 9 and resulting in a frequent appearance of defects in the coil layer 9.
(C) For the purpose of increasing the signal recording density and magnetic recording frequency in recording media, it is required to improve the soft magnetic characteristic of the lower core layer 13 and upper core layer 10 as well as to make them to have such properties as low coercive force and high resistivity at high saturated magnetic flux density. Permalloy that has been the conventional material for forming the lower core layer 13 and upper core layer 10 is not always a satisfactory magnetic material because, although its saturated magnetic flux density is high, its coercive force is relatively high and resistivity is relatively low so that, when the recording frequency is made higher, it results in an increase of eddy current loss and deterioration of soft magnetic characteristic. Meanwhile, U.S. Pat. No. 5,573,863 discloses a soft magnetic material in which a microcrystalline phase of Fe with a bcc crystal structure, and an amorphous phase containing the elements selected from rare earth elements or from Ti, Zr, Hf, V, Nb, Ta and W, and O, are mixed together. This kind of soft magnetic material has a high magnetic permeability at a frequency of hundreds MHz or more as well as a high saturated magnetic flux density of 5 kg or more besides having a high resistivity at low coercive force. It is preferable in the future-coming inductive head for the purpose of high density recording that the lower core layer 13 and upper core layer 10 is formed using such materials excellent in the soft magnetic characteristic as hitherto described. However, the soft magnetic material as described in the afore mentioned U.S. Pat. No. 5,573,863 in which a microcrystalline phase of Fe and amorphous phase comprising metal elements and O are mixed together can not be formed by plating, instead a sputtering method or an evaporation method is only applicable for forming the layers. In the combination read/write thin film magnetic head having a construction as shown in FIG. 5, however, forming the lower core layer 13 by sputtering was so difficult that only a material like permalloy that is adaptable for plating can be used for the soft magnetic material of the lower core layer 13.
The above description will be elaborated hereinafter. When the lower core layer 13 is formed by a sputtering method, a layer of a soft magnetic material is directly formed on the upper gap layer 6 comprising aluminum oxide on the layer of a magnetoresistive element 1. However, it is necessary to eliminate the excess part by an ion milling (dry etching) method for forming the lower core layer 13 into a prescribed configuration as described above after forming a layer of soft magnetic material by a sputtering method. It is a problem that the underlying layer of aluminum oxide is damaged when the layer of soft magnetic material is eliminated by ion milling. Generally speaking, a tolerance of about 5% in the thickness of layers to be eliminated is inevitable when a prescribed thickness of layers are eliminated by the ion milling method. Since the thickness of the underlying upper gap layer 6 is smaller than the thickness of the lower core layer 13, the thin upper gap layer 6 is liable to be damaged due to an error of about 5% in the thickness of layers to be eliminated when the upper gap layer 6 is formed by eliminating a part of the layer of soft magnetic materials formed by sputtering. In addition, since the velocity of milling is slower in the soft magnetic material comprising the lower core layer 13 than in aluminum oxide comprising the upper gap layer 6, the latter is far more liable to be damaged when the layer of the soft magnetic material is eliminated by ion milling.
The gap width of the reading part by the layer of the magnetoresistive element 1 is determined by the thickness of the lower gap layer 3 and upper gap layer 6 in this thin film magnetic head. Therefore, the upper gap layer 6 should be thin in order to enhance the resolution against high density signals. When the upper gap layer 6 is made thin in the thin film magnetic head for enabling readout of the high density signals, the upper gap layer 6 is liable to be largely damaged due to the error in the thickness for eliminating layers by the ion milling and milling rate.
From the discussions above, it can be concluded that the materials having an excellent soft magnetic characteristic as described in U.S. Pat. No. 5,573,863 can not be used in the inductive head, wherein the upper gap layer 6 is disposed on the layer of the magnetoresistive element 1 on which the lower core layer 13 is further formed and the lower core layer 13 also serves as a shield layer of the layer of the magnetoresistive element 1 as shown in FIG. 5, since the lower core layer 13 can be formed only by a plating process, thereby narrowing the selection range for the soft magnetic materials to be used for forming the lower core layer 13.